A Transmission Control Protocol/Internet Protocol (Transmission Control Protocol/Internet Protocol, TCP/IP) is a basis of a contemporary Internet and has been widely applied. With development of an IP-based technology, it is increasingly popular that a user accesses Internet content by using an IP-based mobile communications network such as Long Term Evolution (LTE), a Universal Mobile Telecommunications System (UMTS), or Worldwide Interoperability for Microwave Access (WiMax). A TCP connection between a client and an Internet server needs to be established by using a 3rd Generation Partnership Project (3GPP) network. The client is connected to a mobile communications network by using a radio link. The mobile communications network is usually connected to the Internet server by using a wired network. A status of a wireless communications network fluctuates with time. For example, a data transmission rate and a packet loss rate between the client and the mobile communications network intensely vary with time. On a basis of this, the TCP/IP protocol provides a congestion control mechanism. When the status of the wireless network becomes poor, a corresponding congestion control solution is automatically used according to the TCP/IP, so as to adjust a transmission policy. However, the status of the wireless network changes more intensely than that of the wired network, and a used transmission adjustment policy such as a congestion control policy should be different, so as to improve wireless interface transmission performance, and improve a network throughput. In addition, a TCP connection transmission rate depends, to a large extent, on a rate at which an acknowledgment (ACK) packet is received on a server. A delay between the client and the server not only affects a transmission rate of a normal packet, but also greatly affects a transmission rate of an acknowledgment packet. Therefore, a network proxy technology needs to be introduced to divide a TCP/IP connection between the client and the Internet server into two parts, and a network proxy device establishes a TCP connection to each of the client and the Internet server, so as to implement the TCP connection between the client and the Internet server. In an existing network proxy technology, when a data transmission rate between the Internet server and the network proxy device is greater than a data transmission rate between the network proxy device and the client, or a data transmission rate between the network proxy device and the client is greater than a data transmission rate between the Internet server and the network proxy device, partial data is cached into the network proxy device within a time period.
However, the client is mobile. When moving from a source cell to a target cell, because the client is not handed over in a timely manner for some reasons, the client needs to perform reconnection by using the target cell. After the client is disconnected from the source cell and is reconnected to the target cell, data cached by a network proxy device enabled in the source cell is not sent to the client or the Internet server in a timely manner. According to the existing TCP protocol, the client repeatedly requests retransmission of the data, but the server considers that the client has received the data, and does not perform retransmission; or the server repeatedly requests retransmission of the data, but the client considers that the server has received the data. Consequently, the TCP/IP connection between the client and the Internet server is interrupted, and a service is terminated, thereby reducing TCP connection stability.